Sept 6-14: The Moon meets with four planets
From September 6 to 14, the Moon will pass by Mars, Jupiter, Mercury, and Venus. Watch Mars near the Moon low in the pre-dawn sky on September 6, then Jupiter close to a thin crescent on the morning of September 8. On September 12, an extremely thin Moon crescent will skim past Mercury in bright evening twilight, and on September 14, it will meet Venus.
Image courtesy of Stellarium
September 22: Autumnal Equinox (6:05 p.m. MDT)
The Earth tilts 23.4 degrees from the plane of its orbit, and it holds that tilt in the same direction year-round. As the planet travels around the Sun, the Northern Hemisphere is tipped toward the Sun in June (longest days, summer solstice), away from the Sun in December (shortest days, winter solstice), and balanced sideways in March and September. The two balanced moments are the equinoxes. In September, that is the precise moment the Sun crosses the celestial equator heading south, and the Northern Hemisphere swings from longer days to longer nights. This is the start of astronomical fall. It's different from meteorological fall, which always begins on September 1st and lines up with the calendar months climatologists use to compare seasonal weather. The astronomical version follows the Sun and the Earth’s tilt; the meteorological version follows the calendar. Both are useful, neither is wrong, and the two are usually about three weeks apart.
Image courtesy of NOAA
September 26: Harvest Moon
Every autumn, one full moon rises brighter and earlier than the rest. Its orange glow, hanging low over ripening fields, has been noticed for as long as humans have looked up. We call it the Harvest Moon, the full moon nearest the autumn equinox, usually in late September or early October. Astronomically, the Harvest Moon isn’t different from any other full moon. What makes it special is timing and light. Around the equinox, the angle between the Moon’s path and the horizon is shallow. This means the Moon rises soon after sunset for several nights in a row, rather than about 50 minutes later each night as it does the rest of the year. The result: a few evenings of extended twilight, bathed in bright, golden moonlight. Traditionally, this extra light aided farmers in harvesting their summer-grown crops.
Image courtesy of Old Farmer's Alamanac
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